Aromatic polyetherketones, for example poly(aryl ether ether ketone) (PEEK) or poly(aryl ether ether ketone ketone) (PEEKK) are generally crystalline high-performance engineering thermoplastics exhibiting relatively high chemical and thermal stability. Among these, PEEK is the most widely used material. Its applications include polymeric supports, insulations, membranes, structural articles and matrix materials for thermoplastic composites.
PEEK type polymers are hydrophobic in nature which limits their membrane application e.g. in separation of aqueous solutions. Also, the poor solubility of PEEK type polymers in conventional ordinary solvents makes the manufacture of membranes difficult.
There is a need to modify these polymers to obtain their substituted derivatives having different properties and structure than the basic polymers.
Generally, there are two ways to functionalize polymers. One is the use of a functionalized comonomer during polymerization, such as the addition of chloromethylated styrene in the polymerization of polystyrene. Commercially and in most laboratories, PEEK is prepared by the nucleophilic substitution reaction of hydroquinone with difluorobenzophenone. Thus, functional groups which can undergo a nucleophilic reaction cannot be introduced into the monomer before the polymerization. This severely limits the scope of the functionalized monomer approach.
The second route involves a modification reaction on the preformed polymer. In the second approach, one of the known methods of polymer modification is bulk sulfonation in sulfuric acid, described for example in U.S. Pat. No. 4,419,486 to Rose. However, due to the poor solubility of PEEK (and other polyaryl ether ketones) in normal organic solvents, other types of functionalization are difficult to perform.
While the sulfonated PEEK derivatives have better hydrophilicity and solubility than the basic PEEK, it is difficult in bulk sulfonation to control the degree of substitution (DS) and the uniformity of substitution. Bulk-sulfonated PEEK becomes too hydrophilic when the degree of substitution is over 80%, resulting in severe swelling or dissolution.
To our knowledge, no method of bulk functionalization of PEEK other than sulfonation and chlorosulfonation is known to date. Some surface functionalization reactions have been described in the scientific literature; for example, N. L. Franchina and T. J. McCarthy, Macromolecules 1991, 24, 3045, reported surface modification of PEEK wherein a series of carbonyl selective reactions were carried out on the surface of a PEEK film. These substitutions lead to polymers which no longer contain the ether-ketone sequences.
An alternative to the above classic modification routes is to introduce an inert pendent group into the monomer and to modify this group after its incorporation in the polymer. PEEK polymers with methyl, phenyl and t-butyl substituents have been prepared, as reported by Kricheldorf et al, New Polymeric Mater. 1988, 1,127; Mohanty et al., J. E. SAMPE Symp. 1986, 31, 945; Risse et al. Macromolecules 1990, 23, 4029; and Bennett et al., polymer 1991, 32, 1633. Low molecular weight amine-terminated methyl and t-butyl substituted PEEK's were prepared and used in epoxy/amine resins. These polymers have not been used as the basis for further modification or the preparation of functionalized polyaryl ether ketones.
Methyl derivatives of polyaryletherketones are described in German OS No. DE 3838644 A1 filed Nov. 15, 1988 and in Japanese patent application (kokai) No. 90-188552 filed Jul. 24 1990.